Furthermore, the present invention concerns a method for manufacturing a reinforcement beam, in particular of a curved ring frame segment, for a fuselage cell of an aircraft comprising a synthetic material that is reinforced by at least one fiber laminate.
Furthermore, the present invention concerns a fiber laminate for manufacturing a reinforcement beam, in particular of a ring frame segment, wherein the fiber laminate comprises at least one layer with a first fiber direction and at least one layer with a second fiber direction as well as a further layer with a third fiber direction.
Ordinarily, ring frames are used in airplanes to reinforce the fuselage cells. These ring frames are mostly made of aluminum beams. The manufacturing of longer ring frame segments or circular ring frames with aluminum beams ordinarily causes no particular problems, since the aluminum beams can be adapted comparatively easily to the fuselage curvature of the fuselage cells by bending them.
During flight, such a ring frame having, for example, a Z-shaped cross section for reinforcing a fuselage cell of an aircraft is mainly subjected to shear and/or transverse forces in the region of the vertical beam. The bent beam sections, on the other hand, are mainly subjected to tensile and/or compression forces. The differentiation between shear and/or transverse forces on the one hand and tensile and/or compression forces on the other hand in different portions of the ring frame is largely irrelevant in the case of aluminum ring frames, since metal materials ordinarily have isotropic material properties.
To achieve further weight savings, however, individual components of fiber-reinforced compound materials, in particular carbon fiber-reinforced epoxy resins, are increasingly used in aircraft construction. The mechanical properties of fiber-reinforced compound materials are ordinarily strongly anisotropic, so that the direction of the main mechanical load should preferably coincide with a main fiber direction. In order to accomplish optimum mechanical properties, it is therefore necessary to adapt or adjust in particular the orientation of the fiber reinforcement to the directions of the applied forces.
Considerable difficulties are created in this context by the introduction of a fabric, of fiber bundles or a combination of these in order to accomplish the fiber reinforcement in the case of, for example, components that are round, oval or have the shape of a segment of a circle. The reason for this is that in such cases, it is often indispensable to let at least a main fiber direction run parallel to the circumferential contour of the component, in order to accomplish optimum rigidity.
Once the fiber reinforcement is formed, the actual component, such as a reinforcement beam for forming a ring frame or a ring frame segment, is manufactured using a method known in the art, such as the so-called resin transfer molding (RTM) method. Alternatively, it is also possible to use continuous injection molding for the manufacture.
If the reinforcement of such a component is to be realized with a fabric or the like, then it is possible to line up short fabric strips in sections along the circumference or perimeter. However, this leads to the disadvantage of a relatively large number of seams due to the necessary division into parts. It is possible to reduce the number of seams with an overlapping arrangement of fabric strips, but this leads to thickened portions in the region of the overlaps.
Furthermore, it is possible to accomplish such a fiber reinforcement by wrapping a long fiber or a long fiber bundle several times around the entire component. This approach entails a higher cost, but avoids unnecessary seams in the fiber reinforcement.
Finally, there is the possibility to cut substantially diagonal strips from a section of a fabric course. Such strips that are cut diagonally from a fabric course can be draped, i.e., laid out in a curved manner in a plane without curling up into creases or folds. Therefore, such fabric strips are in principle suitable for a reinforcement of the perimeter of components with small dimensions that are round, oval or have the shape of a circle segment, because in the ideal case only a single seam is caused. However, such strips have the disadvantage that due to the limited width of fabric courses, they can only be fabricated with a limited length, so that larger components, such as ring frames or the like, cannot be manufactured in this manner.